1. Field of the Invention
The invention relates to techniques for flashing fluorescent lamps and, more particularly, to circuitry which either may be placed in the line cord providing power to a fluorescent lamp or which may be shorted across, or included as part of, a starter used with a fluorescent lamp.
2. Description of the Prior Art
Fluorescent lamps have been used for a number of years to provide economical, efficient lighting. Although fluorescent lamps have desirable lighting qualities, the nature of their operation has limited their uses to more or less steady state operation. Either they are operated continuously at full capacity or they are not operated at all. Under certain conditions it would be desirable to flash fluorescent lamps, particularly ultraviolet fluorescent lamps, to the beat of music or other audio signals. It also may be desirable to flash fluorescent lamps, particularly ultraviolet fluorescent lamps, at a predetermined frequency on the order of two or three flashes per second independently of external signals. Unfortunately, prior techniques for flashing fluorescent lamps have not been entirely satisfactory.
Most prior techniques for flashing fluorescent lamps depend upon maintaining electrode heat relatively high during the flashing cycle. In one known technique, separate filament transformers are connected across the electrodes and current to one of the filament transformers is periodically interrupted. This technique functions adequately, but expense of the assembly is higher than desired. Another technique is to periodically change the current flowing through a resistor ballast by use of an incandescent flasher lamp. Unfortunately, this technique is unacceptable because the life of a typical incandescent flasher lamp is only about 20-500 hours, compared with a typical fluorescent lamp life of about 6000 hours.
One technique which has been experimented with in the flashing of fluorescent lamps is to bypass, or short, current across the terminals of the starter. This technique has the advantage of extinguishing the lamp discharge, but preheat current flows through the electrodes keeping them hot enough to emit electrons and prevent life-damaging high cathode fall. At least one prior technique for shorting the lamp terminals requires the removal of the starter and replacement by separate flasher circuitry. Either the lamp operates conventionally or it operates entirely in a flashing mode. This is a considerable limitation on the practical implementation of flashing circuitry for fluorescent lamps.
A desirable approach to flashing fluorescent lamps would be to place a flasher in the line cord powering the lamp, that is, "upstream" of the lamp. This technique would have the advantage of not requiring the modification of existing lamp constructions or lamp-manufacturing equipment. It would be a relatively simple matter to install the flashing circuitry in the line cord of a fluorescent lamp. Prior techniques for flashing fluorescent lamps by employing circuitry located "upstream" of the lamp have had the drawbacks of requiring separate filament transformers or short flasher life, as mentioned previously, or have employed unduly expensive components.
In view of the foregoing problems, it is an object of the invention to provide a flashing fluorescent lamp.
It is another object of the invention to provide a flashing fluorescent lamp requiring a minimum of components to carry out a flashing operation.
It is yet another object of the invention to provide an inexpensive flashing fluorescent lamp.
It is yet another object of the invention to provide a flashing fluorescent lamp in which the life of the lamp and flasher circuitry approximates that of conventional, non-flashing fluorescent lamps.
It is yet another object of the invention to provide a flashing fluorescent lamp wherein flasher circuitry bypasses current past a starter.
It is a still further object of the invention to provide a flashing fluorescent lamp wherein flashing circuitry is included as part of the line cord supplying power to the fluorescent lamp.